The present invention relates to a machine which provides a resisting force for use in electronic- or computer-controlled equipment for exercise, training, or physical therapy.
Exercise has historically fallen into two categories: aerobic exercise and resistance exercise. Aerobic exercise is characterized by low resistance to the user's motion, but maintained at high speed for an extended period of time resulting in increased heartbeat and breathing rates. Resistance exercise, however, involves a greater resistance for shorter periods of time to intentionally break down and regenerate muscle tissue and lead to increased muscle bulk and strength. Equipment for both aerobic and resistance exercise have recently progressed into electronically enhanced versions.
The aerobic machines have progressed more rapidly into electronically enhanced versions due to two characteristics of this type of exercise: (1) relatively low resistance, and (2) intermittently or slowly varying resistance force levels over time.
This progression is evidenced by the recent introduction of electronically controlled rowing machines by Precor and AMF, and by the electronic stationary bicycles available from Bally, and by the computer-monitored moving staircase by Stainmaster.
The progress of electronically enhanced resistance equipment has progressed into mechanical machines of axles, pulleys, chains, wire rope, sprockets, and handlebars which could transmit the user's motion into the raising and lowering of stacks of weights. These machines made resistance exercise more convenient and could isolate individual muscle groups more effectively.
A mechanical enhancement of resistance equipment was patented by Jones [U.S. Pat. No. 3,858,873]. This invention added sophistication to weight-based machines by adding the capability of varying the resistance level as a function of the position of the user's moving member. This advancement is especially important where gravitational forces alone do not result in constant resistance throughout the exercise stroke, as in rotary exercises performed with free weights.
Later, electronic control of resistance began to enhance resistance exercise. Flavell (1973) discloses in U.S. Pat. No. 3,869,121 a machine that provides braking resistance in one direction through the use of an electric brake, and motion in the other direction using, for example, an electric motor or spring. Flavell later introduced [U.S. Pat. No. 4,184,678] an electromechanical machine that could regulate the user's motion against a desired, predetermined, force vs. speed characteristic, thereby creating a speed-programmable device. Still another of Flavell's U.S. patents, U.S. Pat. No. 4,261,562, advanced the speed-programmable device to include a motor with a wound stator interacting with rotating magnets to provide the resistance force. This resistance force is generated by the energy dissipated in an electrical loading of the stator windings. A similar exercise device was disclosed by Dorfman in U.S. Pat. No. 4,602,373 is which two electrically shorted commutator brushes are positioned against a rotating coil to regulate the resistance torque.
Bruder [U.S. Pat. No. 4,518,163] produced a machine that provided braking resistance levels as a stepwise function of the position of the user's moving member. With electronic control, the possibility of having random resistance levels, not predictable by the user, was reduced to practice by Sweeny in U.S. Pat. No. 4,358,105. Having resistance levels increase or decrease adaptively as a function of the user's performance was conceived by Jungerwith and such a machine was disclosed in his U.S. Pat. No. 4,323,237.
Electronic resistance also enables sophisticated monitoring of the user's performance during the exercise process. Barron patented a device [U.S. Pat. No. 3,984,666] which could accumulate and display calories expended during exercise using a resistance mechanism based on an alternator. Relyea [U.S. Pat. No. 4,408,613] extended this concept by having an audio-visual system instruct the user while controlling resistance through an electric brake. A motor-clutch combination was proposed as a resistance mechanism by Fulks in U.S. Pat. No. 4,569,518. The variable clutch selectively applies torque from the motor to the user during exercise.
The demand for the user himself or his trainer, coach, or therapist to program individualized resistance profiles as a function of position was partially fulfilled by Ariel, as revealed in his U.S. Pat. No. 4,354,676. The programmability of a resistance machine represented an advancement in flexibility of resistance exercise. This system could also accumulate and display characteristics and statistics of the user's exercise. A later U.S. Pat. No. 4,544,154 by Ariel employed feedback control circuitry, leaving the computer more computational time for monitoring and graphical display. This patent specified a hydraulic cylinder as the resistance device.
Although the Ariel machine is programmable, it does assume the availability of a resistance mechanism that can respond to electrical signals. Much less work is apparent in the provision of a generalized, electronic resistance device having the characteristics needed to (1) be adaptable to a broad range of exercise machines, even retrofitted to existing weight-based systems, and (2) be capable of interfacing to electronic or computer based control in a variety of exercise modes. To fulfill need (1) the resistance device must be capable of providing potentially high levels of resistance. To fulfill need (2) the electronics and mechanical system must have a short response time (i.e. the time between a force resistance level is commanded by a computer or electronic circuit and the time that the resistance force is actually available).
Fulfilling both of these needs simultaneously represents an engineering challenge due to electrical and mechanical inertia forces typically present in electric brakes or other force-generating devices. Mechanical inertia exists in the form of static and dynamic friction and rotational mass of the gear trains. Electrical inertia exists in the inductance of coils needed to generate electromagnetic forces. Although the Ariel patent does suggest using computer control to remove these anamolous forces, it does not discuss the fast response required of the resisting device.
The response-time problem was addressed in European patent application No. 0060302, by applicant Mitsubishi Kinzoku Kabushiki Kaisha, entitled "Muscle Training and Measuring Machine", filed on May 5, 1981. A solution to the problem, presented in the patent application, was the use of a hydraulic servo amplifier. The resulting invention was a hydraulic-based resistance mechanism capable of responding quickly to electrical signals. This patent application also revealed the necessity of quick response for most forms of sophisticated resistance exercise including isokinetic and isometric. This patent application also faulted motor- and brake-based resistance mechanisms for having resistance characteristics that are difficult to control, mentioning specifically friction and rotary mass of the rotor and gears. Although this invention claimed to solve the inertia problems for hydraulic-based resistance system, no known solution for brake-based systems is available. Brakes have advantages over hydraulics and motor based systems. Hydraulic cylinders contain a fluid that can leak and needs to be replaced periodically. Motors have a greater change of violating the user's safety than brakes. Motors create motion, but brakes only resist motion created by the user. If the user becomes weakened during exercise, a motor will continue to burden the user, possibly to the point of injury. Free weights as well as motors have this safety disadvantage relative to brakes.
Hence, the need does exist for a fast responding brake-based resistance mechanism, which is capable of high resistance forces and is adaptable to all modes of exercise in a safe manner. These needs are satisfied by the invention disclosed herein. This invention difers from the Flavell machine disclosed in U.S. Pat. No. 4,261,562 (previously mentioned) in that a brake is used to control forces directly rather than by varying the load on an electric motor acting as a generator. Load variation only permits varying the constant of proportionality between force and speed, whereas an electric brake can generate a force independent of, or arbitrarily dependent on, speed. This invention teaches a fast responding control system for a brake-based machine.
Three types of electric brakes are of common availability. The first type is the friction brake, in which an electric current flows through a coil of wire in the stationary portion (stator) producing a magnetic field which pulls the moving portion (rotor) in contact with the stator. The force of contact resists the motion of the rotor through friction properties of the material in contact.
The second type of electric brake is the hysteresis brake. In a hysteresis brake, an electric current flowing in a coil creates a large magnetic field in a cylindrically shaped gap. The rotor contains appreciable area which rotates within this gap. Motion of the rotor causes periodic magnetization and demagnetization of the rotor material. Each magnetization cycle involves an energy loss, and this loss generates a force resisting the motion of the rotor.
A third type of brake is the particle brake, which combines the features of the hysteresis and friction brakes. Small particles are present in the gap between the rotor and the stator. The resistance is produced by both friction of the particle motion and the repeated reverse magnetization of the particles. Greenhut disclosed in U.S. Pat. No. 4,620,703 a machine that employs a particle brake generating a resistance in both directions of exercise motion. Greenhut also mentioned the response time problem of brakes, and thereby proposed the more efficient particle brake combined with a transmission system having a high gear ratio.
The frictional properties of materials used in friction brakes tend to vary with rotor speed, making the force vs. current characteristic non-ideal. The difference between static and dynamic friction causes an undesirable jerky motion when exercising with a friction-brake-based resistance machine.
Hysteresis brakes tend to have a more constant force vs. velocity relationship, but the absence of material contact causes the hysteresis brake to be less efficient than the friction brake in producing a torque in response to a given input current. The loss of efficiency is regained in using larger coils, but this in turn increases the electrical inertia, or inductance, which is a problem when trying to change electrical current levels (and hence resistance force levels) quickly during the exercise process.
The desire to use smaller, lower cost, electric brakes can be fulfilled by using gear trains in the mechanical coupling of the user's motion to the rotary motion of the brake. The gear train causes the brake's rotor to rotate more quickly, hence magnifying the resistance apparent to the user. The gear train also introduces friction regardless of the type of brake used. Also, the rotary mass of large gears can be particularly noticeable at the start and end of the exercise stroke. At the start of the stroke, the user must exert more to bring the system up to a desired exercise speed. At the end of the stroke, the kinetic energy of the system, and not the user's exertion, keeps the system in motion. Hence, rotary mass interferes with the exercise process.
The problems discussed previously, i.e. those of inductance and rotary mass can be solved through the use of this invention. In addition, this invention can provide exercise modes not previously available from brake-based machines. The prior art brake-based resistance machines available from Paramount provide slowly varying forces, and hence is limited to a single mode of exercise (isotonic). This invention, with the addition of sensors and compensation circuits, further improves over the prior art by making possible brake-based resistance with additional exercise modes, including isokinetic, isometric, and viscous.
Isokinetic and isometric exercise modes are well known. Isokinetic means "constant speed", and isokinetic resistance machines resist the user's motion to the extent necessary (and no further) to maintain a constant speed of motion. In brake-based resistance systems, no resistance is applied until the user reaches the set speed, and is henceforth maintained at that speed. Isometric means "constant position" and isometric machines oppose the user's exerted force such that very little motion is produced. In practical brake-based resistance machines, isometric exercise is equivalent to a very slow isokinetic exercise. A single position cannot be maintained exactly due to the inability of the brake to produce motion. Viscous resistance is not as well known, but is also a desirable exercise mode. In viscous resistance, the resulting force is proportional to the speed of motion. This exercise mode is unique in the smoothness of motion created. Hydraulic cylinders, in which a fluid is pushed through a small hole produces viscous resistance naturally. This invention permits viscous resistance to be simulated accurately using an electric brake.